Web Components as Pattern Libraries: Building the element

One of the things that have caught my attention about web components is how easy it is to adapt them as pattern libraries and design libraries. Because we can isolate the style and scripts for each individual component and compose larger UI elements from smaller elements, Web Components are ideal for this type of work.

Before we can delve into pattern and design libraries we need to design what they are. So here we go:

A design library completely covers an element or a pattern: what it intended purpose is, how it looks, what behaviors and styles are available for the element and how we use it.

The idea is that wherever we use an element from the library we know what it’ll look like and how it will behave. This allows designer to create consistent interfaces for their applications.

Web Components make it easier to create reusable elements. we can create elements where the content is assigned to different areas of the template and, unlike template engines like Moustache and Handlebars, this is all baked into the platform. Add ShadowDOM for encapsulation and custom styles built with css variables and you have a full suite of tools to create your patterns and libraries.

For the examples in this essay I will use Polymer 1.x. It may not be an ideal platform for all pattern libraries but I think it illustrates some of the concepts I’m trying to make. We can also take advantage of some advanced CSS features to make sure we don’t have to style

Atomic web design

I will use a modified version of Atomic Web Design as the underlying principle and rules to build the pattern library.

Periodic Table of HTML Elements shows that all HTML elements are organized around a function.

Because all the content that we use for the web starts from the same basic components we can use a similar building pattern to what nature uses, going from the simplest to the most complex.

Atomic design is a methodology composed of five distinct stages working together to create interface design systems in a more deliberate and hierarchical manner. The five stages of atomic design are:

1. Atoms
2. Molecules
3. Organisms
4. Templates
5. Pages

The main difference in my web component based approach is that I’ll concentrate on Molecules and higher organisms. Atoms (all HTML Elements) atoms are part of each molecule and can be changed by changing the component.

We’ll look at how to customize a component later in the article but one of the great advantages of web components is that you can create one customizable molecule to handle many layouts and color arrangements without having to create customized versions of the element.

Building a molecule using Polymer

Prep work

Before we can build a custom molecule we have to build a Polymer element. This requires Bower in order to install the dependencies for our element. Install Bower as a global Node application if you haven’t done so already.

npm install -g bower

Once Bower is installed run the initialization command and answer the questions when prompted.

bower init

For a normal Polymer Application I’d suggest installing the Polymer CLI. This will make it easier to work with Polymer and the Paper and Iron element collections. Because I don’t want to tie the pattern library to a style (Material Design) or a given philosophy of how to build molecules we’ll go with the manual way instead.

At the root of the application, run bower to install the Polymer library.

bower install --save Polymer/Polymer

Then create a directory for your component and change to the directory.

The first thing we do in our Polymer element is to import the Polymer library into the element using HTML Imports.

dom-module is the basic structure of our Polymer element. Its only attribute is id which we will match inside the Polymer element registration.

The only restriction for Polymer and Web Component names is that they must have a dash (-) in the name to differentiate them from current or future HTML elements.

we follow the declaration with a style tag that will contain all the styles specific to the element. We will cover styling in more detail later but for now we’ll place a style tag in the template. The remainder of the script is the HTML tags that make up the structure of your element.

Next we build a template tag containing the structure of our pattern. The templates are built with the same atoms that we use in our everyday web development. We learn a different way to build the atoms and molecules and the higher order elements of Atomic Web Design but not a different templating language like moustache, handlebars or others.

This is one of the main reasons why I chose web components and Polymer in particular.

The last part of the element is a script where we register the Polymer element.

In the script we first create a Polymer object. The first attribute, is uses the ID of the dom-module tag we opened the document with and tells the HTML parser the name of the element. We then create attributes for each of the items we enclosed in {{}} when we declared in the element. These elements are bound to what happens in the element so we can create different elements with different attributes without having to hard code them in

There is a lot we can do with this element. Properties define properties and methods for our element’s prototype. hostAttributes define attributes that are included in our element when they are first created; for example they can be attributes we use to style the element.